The present invention relates to a fastener driver, and more particularly, to an electric fastener driver.
A compressed air type fastener driver such as a nail gun has been known. Compressed air generated by a compressor is used as a power source for the fastener driver. However, the use of a compressor is a prerequisite for compressed air type fastener drivers. Therefore, when operating a fastener driver while moving the driver from the ground floor to the first floor of a building, the compressor needs to be moved along with the fastener driver. In other words, such a combination lacks mobility. Additionally, a space needs to be provided for placing the compressor. However, sites of fastener driver operation do not always have a flat area for placing a compressor. In other words, sites of operation are limited for fastener driver that require the use of a compressor.
Electric fastener drivers adapted to drive a solenoid coil as main drive source, using electric power as motive power, are known that are less subject to limitations in terms of sites of operation and mobility. However, since the electric efficiency of solenoid coils is rather poor and between 5 and 20%, fastener drivers adapted to use a solenoid coil are inevitably heavy and bulky when the required drive power is large. More specifically, a fastener driver using a solenoid coil is about three times as heavy as a compressed air type fastener driver having a same output power. Then, to hold such a fastener driver by hand for a long time in order to drive nails has been difficult.
In an attempt to improve the electric efficiency of electric fastener drivers using a solenoid, a fastener driver using a flywheel has been proposed in laid open Japanese Patent Application Kokai Nos. H8-197455 and H6-278051. The flywheel is driven by electric power to drive a fastener exploiting the rotary kinetic energy accumulated in the flywheel.
For a fastener driver using a flywheel to drive a nail with reduced reaction force, the kinetic energy accumulated in the flywheel is necessarily be transmitted to the driver mechanism as motive power within the time to be spent for driving the nail (tens of several milliseconds). A fastener driver as described in Japanese Patent Application Kokai Nos. H8-197455 has a mechanism including a flywheel, a solenoid, a plurality of cams, a clutch and a ball.
The ball is accommodated in the groove of a ball inner pan and that of a ball outer pan and is nipped between the ball inner pan and the ball outer pan. The grooves have a varying depth and the ball moves in the groove relative to the ball inner pan and the ball outer pan as the ball outer pan is turned relative to the ball inner pan. When the ball is held in a shallow part of the grooves, the ball inner pan and the ball outer pan are relatively remote from each other, to render the clutch on. When, on the other hand, the ball is held in a deep part of the grooves, the ball inner pan and the ball outer pan are relatively close to each other, to render the clutch off.
The electric fastener driver adapted to drive a nail, exploiting the kinetic energy of such a flywheel shows an excellent electric efficiency between 50 and 70% and the nail driving energy can be boosted by raising the number of revolutions per unit time of the flywheel. Thus, such an electric fastener driver can be made to be only one and a half times heavier than a compressed air type fastener driver having the same output power.
However, in the known improved electric fastener driver, the clutch is turned on and off as the balls move in the grooves and the ball does no move uniformly in the grooves. In other words, to turn on and off the clutch precisely at a given rotary position of the ball outer pan relative to the ball inner pan has been difficult.